Glow plug connection for model engines

ABSTRACT

A glow plug ( 10, 150, 170, 190, 250 ) is provided for use in a model engine  12  and for connecting to a glow plug clip ( 30 ). The glow plug ( 10, 150, 170, 190, 250 ) includes a coil ( 38 ) having spaced apart first and second ends ( 42, 44 ), a first conductor ( 34 ) coupled to the first end ( 42 ) of the coil ( 38 ), and a second conductor ( 40 ) coupled to the second end ( 44 ) of the coil ( 38 ). The second conductor ( 40 ) includes a body and a glow plug clip-retaining portion ( 32, 152, 172, 192, 252 ) and the glow plug clip-retaining portion is defined by an indentation ( 70, 72, 176, 196, 256 ) in the body.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national application of internationalapplication Ser. No. PCT/US98/15105 filed Jul. 22, 1998, which claimspriority to U.S. provisional applications Ser. Nos. 60/053,744 and60/057,548 filed Jul. 25, 1997, and Aug. 29, 1997, respectively.

This invention relates to engines for model aircraft, cars, boats, andthe like, and particularly to model engines having a glow-style ignitionsystem. More particularly, the present invention relates to an improvedconnection between a model engine glow plug and a glow plug clip used totransmit electrical power from an energy supply to the glow plug whenstarting the model engine.

Most current-day engines used in model airplanes, cars, and boats arecalled “glow-ignition” engines because they rely on a hot, glowingplatinum-alloy coil located within a combustion chamber of the engine toignite an air/fuel mixture within the combustion chamber. The pressuredeveloped by the burning air-fuel mixture typically displaces a pistonwhich in turn drives a rotary output shaft thereby producing usablemechanical power. The fuel used in a glow-ignition engine is usuallycomprised of alcohol, castor oil, and nitromethane. Proper fuelcombustion is maintained not only by the high temperature of the glowingplatinum coil, but also by the catalyzing action of the platinum metalon the fuel/air mixture. The platinum coil in a glow-ignition engineburns out occasionally and so is generally manufactured as part of anassembly called a glow plug which can be easily removed from the engineand replaced.

According to the present invention, a glow plug including a glow plugclip-retaining portion is provided for use on model engines. The glowplug clip-retaining portion is an indentation or recess formed in asurface of the glow plug.

In a preferred embodiment, the glow plug clip-retaining portion is acircumferentially extending lip and a circumferentially extending slotformed on an exterior surface of the glow plug adjacent to thecircumferentially extending lip. This circumferentially extending slotis receptive to a locking mechanism on a variety of popular conventionalglow plug clips already in service.

A glow plug clip-engaging surface is provided on an upper end of theglow plug adjacent to the circumferentially extending lip to facilitateapplication of the glow plug clip to the glow plug. The holding andcentering power of the glow plug clip-retaining portion is improved bysloping the sides of the circumferentially extending retaining slotthereby encouraging the glow plug clip to lock tightly to the center ofthe circumferentially extending retaining slot or to the back side ofthe circumferentially extending retaining lip.

In preferred embodiments, the glow plug clip-retaining portion iscircular in cross section and manufactured easily on automatic screwmachines. In addition, in preferred embodiments, the glow plugclip-retaining portion can be used on glow plugs of a variety of sizesand configurations.

Additional features and advantages of the invention will become apparentto those skilled in the art upon consideration of the following detaileddescription of preferred embodiments which exemplify the best mode ofcarrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a side elevational view, with portions cutaway, of a glow plugpositioned to lie in a model engine and a glow plug clip that provideselectrical current to the glow plug;

FIG. 2 is a partial sectional view of a glow plug showing the glow plugbeing formed to include a circumferentially extending retaining slot anda circumferentially extending retaining lip that define a glow plugclip-retaining portion in accordance with the current invention;

FIG. 3 is a side elevation view, with portions cutaway, of the glow plugclip and glow plug shown in FIGS. 1 and 2;

FIG. 4 is an enlarged side elevation view, with portions cutaway, of theglow plug clip shown in FIG. 3 partially engaging the glow plugclip-retaining portion of the glow plug shown in FIG. 3;

FIG. 5 is an enlarged side elevation view, with portions cutaway, of theglow plug clip shown in FIGS. 3 and 4 fully engaging the glow plugclip-retaining portion of the glow plug;

FIG. 6 is a side elevational view of another preferred embodiment of aglow plug showing the glow plug having a glow plug clip-retainingportion defined by circumferentially extending retaining lip and acircumferentially extending retaining slot;

FIG. 7 is a side elevational view of yet another preferred embodiment ofa glow plug showing the glow plug having a glow plug clip-retainingportion defined by a plurality of shallow annular grooves formed in theglow plug body;

FIG. 8 is a sectional view of the glow plug of FIG. 7;

FIG. 9 is a side elevational view of yet another preferred embodiment ofa glow plug showing the glow plug having a glow plug clip-retainingportion defined by a diamond knurl pattern;

FIG. 10 is a perspective view of a glow plug for use with relativelylarge model engines showing the glow plug having hexagonal wrench flatsand a threaded base;

FIG. 11 is a sectional view of the glow plug of FIG. 10, taken alongline 11—11 of FIG. 10; and

FIG. 12 is a side elevation view of a glow plug similar to the glow plugshown in FIGS. 10 and 11 showing the glow plug including a glow plugclip-retaining portion.

DETAILED DESCRIPTION OF THE DRAWINGS

A glow plug 10 for use on a model engine 12 is shown in FIG. 1. Theengine 12 includes a heat sink 14, an engine cylinder 16, a combustionchamber 18, an output shaft 20, and a carburetor 22. The heat sink 14includes first and second heat sink portions 24, 26 that threadinglyengage each other and a glow plug-receiving aperture 28 extendingthrough first heat sink portion 24. Glow plug 10 is positioned to lie inglow plug-receiving aperture 28 and is secured between first and secondheat sink portions 24, 26 as shown in FIG. 1.

A glow plug clip 30 is also shown in FIG. 1. Glow plug clip 30 isadapted to engage glow plug 10 to provide an electric current throughglow plug 10 as shown, for example in FIGS. 4 and 5. The electriccurrent causes combustion of an air/fuel mixture that is present incombustion chamber 18 of model engine 12.

As shown in FIG. 2, glow plug 10 is generally round in cross section andincludes a glow plug clip-retaining portion 32, an inner pole orconductor 34, an electrical insulator 36, a coil or conductor 38, and abody or outer conductor 40. In preferred embodiments, coil 40 is formedof a platinum-alloy wire and includes a first end 42 connected to innerpole 34 and a second end 44 connected to body 40. Application of avoltage to inner pole 34 and body 40, as may be developed by an electricbattery 46, induces an electric current through coil 38 causing coil 38to glow at a very high temperature. When situated within combustionchamber 18 of model engine 12, glowing coil 38 can initiate thecombustion of the air/fuel mixture in combustion chamber 18. Theplatinum-alloy of coil 38 operates to catalyze and maintain the air/fuelcombustion reaction after electric battery 46 is disconnected from coil38.

Body 14 extends along a longitudinal axis 48 and includes a top end 50,a bottom end 52, a mounting flange 54 positioned to lie at bottom end52, a cylindrical side wall 56 having a lower end 58 connected tomounting flange 54 and an upper end 60 positioned to lie at top end 50,an outer surface 62 facing away from longitudinal axis 48, and an innersurface 64 defining an inner pole-receiving aperture 66 extendingbetween top end 50 and bottom end 52 as shown, for example, in FIG. 2.Inner pole 34, electrical insulator 36, and coil 38 extend throughportions of inner pole-receiving aperture 66. The mounting flange 54 ispositioned to lie between first and second heat sink portions 24, 26 asshown in FIG. 1. First heat sink portion 24 may also be referred to as aclamp ring because it screws downwardly onto mounting flange 54 tosecure glow plug 10 to model engine 12.

Glow plug clip-retaining portion 32 is defined by an indentation orrecess in cylindrical side wall 56. More specifically, glow plugclip-retaining portion 32 is defined by a circumferentially extendingretaining lip 68 formed in cylindrical side wall 56 of body 40 and acircumferentially extending retaining slot 70 formed in cylindrical sidewall 56 adjacent to circumferentially extending retaining lip 68. Thecircumferentially extending retaining slot 70 is defined by spaced-apartfirst and second slot walls 72, 74 that converge inwardly towardlongitudinal axis 48 to a center 76 of circumferentially extendingretaining slot 70. First slot wall 72 extends between circumferentiallyextending lip 68 and center 76, and second slot wall 74 extends fromcenter 76 away from inner surface 64 and toward bottom end 52 as shown,for example, in FIG. 2.

The circumferentially extending retaining lip 68 is positioned to liebetween top end 50 and circumferentially extending retaining slot 70.The body 40 further includes a glow plug clip-engaging surface 78 havinga first end 80 positioned to lie adjacent to top end 50 and a second end82 positioned to lie adjacent to circumferentially extending retaininglip 68. The glow plug clip-engaging surface 78 is angled with respect tolongitudinal axis 48 so first end 80 is positioned to lie between secondend 82 and longitudinal axis 48.

First and second slot walls 72, 74 extend relative to longitudinal axis48 along slot wall angles 84, 86, respectively, and glow plugclip-engaging surface 78 extends relative to longitudinal axis 48 alongglow plug clip-engaging surface angle 88. First and second slot walls72, 74 cooperate to define a semicircle having a slot radius 96. Inpreferred embodiments of the present invention, body 40 includes anouter diameter 90 of about 0.33 inch (0.84 cm) to 0.35 inch (0.89 cm), aslot diameter 92 of about 0.295 inch (0.75 cm) to 0.325 inch (0.83 cm),and a height 94 between bottom end 52 of body 40 and circumferentiallyextending retaining slot 70 of about 0.33 inch (0.84 cm) or more. Slotradius 96 is about 0.03 inch (0.08 cm). The circumferentially extendingretaining slot 70 includes a slot depth 93 of about 0.02 inch (0.5 mm)deep, glow plug clip-engaging surface angle 88 is about 20 degrees, andslot wall angles 84, 86 are about 68 degrees.

FIGS. 3-5 illustrate the application of a glow plug clip 30 to glow plug10. As shown in FIG. 3, glow plug clip 30 has an inner sleeve 98, whichis generally round in cross section, an outer sleeve 110, a thumb button112 connected to inner sleeve 98, a finger grip 114 connected to outersleeve 110, a spring 116 extending between thumb button 112 and fingergrip 114, and a longitudinal axis 134. Inner sleeve 98 includes a firstend 124 connected to thumb button 128 and a second or collect end 126spaced apart from first end 124. Outer sleeve 110 includes a first end128 connected to finger grip 114 and a second end 130 spaced apart fromthe first end 128. A user may move outer sleeve 110 relative to innersleeve 98 by gripping thumb button 112 and finger grip 114 andcompressing spring 116. Glow plug clip 30 further includes an inner post118 and electrical wires 120, 122 connected to a battery 46 and to eachof inner sleeve 98 and inner post 118.

To attach glow plug clip 30 to glow plug 10, an operator of a modelengine 12 holds glow plug clip 30 in one hand with the index and ringfinger positioned below finger grip 114 and thumb pressing on thumbbutton 112. When the operator presses thumb button 112 toward fingergrip 114, collect end 126 of inner sleeve 98 extends downward relativeto second end 130 of outer sleeve 110 as shown in FIG. 4. Collect end126 of inner sleeve 98 is formed to include a plurality of longitudinalslits 132 that allow collect end 126 of inner sleeve 98 to expandslightly to accommodate entry of glow plug 10 within inner sleeve 98.Glow plug clip-engaging surface 78 of glow plug 10 facilitates entry ofupper end 60 of glow plug 10 into inner sleeve 98 of glow plug clip 30by centering and expanding collect end 126 of inner sleeve 98 aroundupper end 60 of glow plug 10.

As shown in FIG. 5, when the operator releases thumb button 112 andfinger grip 114, return spring 116 (shown in FIG. 3) pushes outer sleeve110 downward away from thumb button 112 over collect end 126 of innersleeve 98 to secure glow plug 10 inside of glow plug clip 30 where innerpole 34 of glow plug 10 makes electrical contact with inner post 118.Second end 130 of outer sleeve 110 is tapered slightly and compressescollect end 126 of inner sleeve 98 into glow plug clip-retaining portion32 of glow plug 10 as outer sleeve 110 is pushed downward over collectend 126 of inner sleeve 98 thereby locking glow plug clip 30 onto glowplug 10. Electrical current from a battery 46 passes serially throughelectrical wire 120, inner post 118, inner pole 34, coil 38, bodyportion 40, inner sleeve 98, and electrical wire 122 when starting modelengine 12 having glow plug 10.

As discussed above, first and second slot walls 72, 74 are defined byslot wall angles 84, 86, respectively. In alternative embodiments of thepresent invention, a square-shaped glow plug clip-retaining slot (a slotwith first and second slot wall angles set to ninety degrees relative tothe longitudinal axis) could adequately retain a glow plug clip on aglow plug. First and second slot walls 72, 74 induce collect end 126 ofinner sleeve 98 of glow plug clip 30 to slide toward center 76 ofcircumferentially extending retaining slot 70 thereby producing apositive locking action. With collect end 126 of inner sleeve 98 of glowplug clip 30 centered within circumferentially extending retaining slot70, longitudinal axis 134 of glow plug clip 30 and longitudinal axis 48of glow plug 10 are maintained in substantially collinear relation asshown, for example, in FIG. 5. Second slot wall 74 assists inmaintaining longitudinal axis 134 of glow plug clip 30 and longitudinalaxis 48 of glow plug 10 in substantially collinear relation. First slotwall 72 of circumferentially extending retaining slot 70 alsofacilitates removal of glow plug clip 30 from glow plug 10 by expandingcollect end 126 of inner sleeve 98 when inner sleeve 98 is pulled awayfrom glow plug 10.

Another preferred embodiment of a glow plug 150 having a glow plugclip-retaining portion 152 and body 154 is shown in FIG. 6. Glow plug150 is identical to glow plug 10 except for glow plug clip-retainingportion 152 and body 154. Components of glow plug 150 that are identicalto components of glow plug 10 are identified with identical referencenumbers.

Glow plug clip-retaining portion 152 of glow plug 150 is identical toglow plug clip-retaining portion 32 of glow plug 10 except that glowplug clip-retaining portion 152 does not include second slot wall 74found in glow plug 10. Glow plug clip-retaining portion 152 is definedby an indentation provided by first slot wall 72.

Accordingly, body 154 of glow plug 150 includes a cylindrical side wall156 that includes diameter 92 between mounting flange 54 and glow plugclip-retaining portion 152 instead of diameter 90 as in cylindrical sidewall 56 of body 40 of glow plug 10. Glow plug 150 does not include asecond slot wall 74 as found in glow plug 10 because it is not requiredto retain glow plug clip 30 on glow plugs 10, 150.

Another preferred glow plug 170 having a glow plug clip-retainingportion 172 and body 174 is shown in FIGS. 7 and 8. Glow plug 170 isidentical to glow plugs 10, 150 except that glow plug clip-retainingportion 172 and body 174 are different from glow plug clip-retainingportions 32, 152 and bodies 40, 154. Components of glow plug 170 thatare identical to components of glow plugs 10, 150 are identified withidentical reference numbers.

Glow plug clip-retaining portion 172 includes an indentation or recessin the form of a plurality of circumferentially extending grooves 176formed in body 174. The plurality of circumferentially extending grooves176 are receptive to collect end 126 of inner sleeve 98 of glow plugclip 30. The plurality of circumferentially extending grooves 176 doesnot extend inwardly toward longitudinal axis 48 as far as first andsecond angled slot walls 72, 74 of glow plugs 10, 150. Body 174 of glowplug 170 includes a cylindrical side wall 178 having an outer diameter180 equal to outer diameter 90 of glow plugs 10, 150, however,cylindrical side 178 includes a thickness 182 that is less than athickness 184 of cylindrical side wall 56 as shown, for example, inFIGS. 2 and 8. The thin cylindrical side wall 178 of glow plug 170permits more room for inner pole 34 and reduces the weight of glow plug170.

The plurality of circumferentially extending grooves 176 may be formed,for example, during a cutting or knurling operation. The plurality ofcircumferentially extending grooves 176 may be in the form of annularrings, as shown in FIGS. 7 and 8, or spiral thread-like grooves (notshown).

Another preferred glow plug 190 having a glow plug clip-retainingportion 192 and body 194 is shown in FIG. 9. Glow plug 190 is identicalto glow plug 170 except that glow plug clip-retaining portion 192 isdefined by indentations or diamond knurl patterns 196 formed in body 194of glow plug 190 as shown in FIG. 9. Components of glow plug 190 thatare identical to components of glow plug 170 are identified withidentical reference numbers.

In the drawings, glow plugs 10, 150, 170, 190 are compatible withcertain commercially available glow plug clips such as the KwikKlip II™manufactured by DuBro Manufacturing Company of Wauconda, Ill.

While glow plugs 10, 150, 170, 190 are generally intended for use withsmall model engines 12 below about 0.10 cubic inch (1.6 cubiccentimeters) displacement, other glow plugs, such as an OS No. 8 glowplug produced by OS Engines of Japan is designed for larger modelengines (not shown). Glow plug 210, shown in FIGS. 10 and 11, isillustrative of the OS No. 8 Glow Plug. Glow plug 210 has body portion212, hexagonal wrench flats 214, inner pole 216, threaded section 218,and coil 220. Coil 220 extends between and is attached to inner pole 216and body 212. As shown in FIG. 11, glow plug 210 has electricalinsulators 222, 224 separating inner pole 216 from body 212 so that avoltage applied to inner pole 216 and body 212 induces a current in coil220. Wrench flats 214 are provided to engage a wrench or other tool whentightening or loosening glow plug 210 in a model engine.

Currently available glow plug clips, such as glow plug clip 30 shown inFIGS. 1 and 3, must slide over an upper end 226 of wrench flats 214 tolock onto corners 228 positioned to lie on a lower end 230 of wrenchflats 214. The maximum radial size of wrench flats 214 is thereforeconstrained by the inside dimensions of inner sleeve 98 of glow plugclip 30. In some applications, such as on very large model engines andspecialty racing engines, it is desirable to manufacture a glow plugfrom a large diameter bar stock, in which case the radial dimensions ofthe wrench flats may exceed the allowable size of standard glow plugclips.

A glow plug 250 configured in accordance with the current invention foruse with larger model engines is shown in FIG. 12. Glow plug 250 isidentical to glow plug 210 except that glow plug 250 includes a glowplug clip-retaining portion 252 appended to upper end 226 of wrenchflats 214. The glow plug clip-retaining portion 252 is defined by anindentation or recess in body 212. The glow plug clip-retaining portion252 includes a circumferentially extending retaining lip 254 formed inbody 212 and a circumferentially extending retaining slot 256 formed inbody 212 adjacent to circumferentially extending retaining lip 254. Thecircumferentially extending retaining slot 256 is defined by first andsecond slot walls 258, 260 that converge inwardly toward longitudinalaxis 262 to a center 264 of circumferentially extending retaining slot256. First slot wall 258 extends between circumferentially extendingretaining lip 254 and center 264, and second slot wall 260 extends fromcenter 264 away from longitudinal axis 262 and toward wrench flats 214as shown in FIG. 12.

The body 212 further includes a top end 266, a bottom end 268, and aglow plug clip-engaging surface 270 having a first end 272 positioned tolie adjacent to top end 266 and a second end 274 positioned to lieadjacent to circumferentially extending retaining lip 254. The glow plugclip-engaging surface 270 is angled with respect to longitudinal axis262 so first end 272 is positioned to lie between second end 274 andlongitudinal axis 262.

Glow plug clip-retaining portion 252 is separated from wrench flats 214,so the size of wrench flats 214 has no operational effect on theapplication of a glow plug clip 30 to glow plug 250. In alternativeembodiments of the present invention, glow plug clip-retaining portionssimilar to glow plug clip-retaining portions 152, 172, shown in FIGS.6-8, may be appended to the upper end of the wrench flats.

Although this invention has been described in detail with reference tocertain embodiments, variations and modifications exist within the scopeand spirit of the invention as described and defined in the followingclaims.

What is claimed is:
 1. A glow plug for use in a model engine and forconnecting to a glow plug clip, the glow plug comprising a conductor,and a body coupled to the conductor, the body including a glow plugclip-retaining portion defined by an indentation.
 2. The glow plug ofclaim 1, wherein the indentation is a semi-circular shaped groove in thebody.
 3. The glow plug of claim 1, wherein the indentation is aplurality of grooves in the body.
 4. The glow plug of claim 3, whereinthe plurality of grooves extends circumferentially around the body. 5.The glow plug of claim 1, wherein the body includes an outer surfacefacing away from the longitudinal axis, a top end, a bottom end, and afirst slot wall, the first slot wall includes spaced-apart first andsecond ends, the first slot wall extends along an angle so that thesecond end of the first slot wall is positioned to lie between the firstend of the first slot wall and the longitudinal axis, and the first slotwall defines the indentation.
 6. The glow plug of claim 5, wherein thebody further includes a second slot wall that includes spaced-apartfirst and second ends, the second slot wall extends along an angle sothat the second end of the second slot wall is positioned to lie betweenthe first end of the first slot wall and the longitudinal axis, and thefirst and second slot walls define the indentation.
 7. The glow plug ofclaim 6, wherein the second ends of the first and second slot wallsconverge at a center of the indentation.
 8. The glow plug of claim 5,wherein the body further includes a retaining lip positioned to liebetween the top end of the body and the first end of the first slotwall.
 9. The glow plug of claim 5, wherein the body further includes aglow plug clip-engaging surface having spaced-apart first and secondends, the second end of the glow plug clip-engaging surface ispositioned to lie between the longitudinal axis and the first end of theglow plug clip-engaging surface.
 10. The glow plug of claim 9, whereinthe second end of the glow plug clip-engaging surface is contiguous withthe top end of the body.
 11. The glow plug of claim 9, wherein the bodyfurther includes a retaining lip positioned to lie between the first endof the first slot wall and the first end of the glow plug clip-engagingsurface.
 12. The glow plug of claim 1, wherein the indentation extendscircumferentially about the body.
 13. The glow plug of claim 1, whereinthe indentation that defines the glow plug clip-retaining portion isspaced apart from the inner pole.
 14. The glow plug of claim 1, whereinthe body includes a mounting flange adapted to mount to a model engineand the indentation that defines the glow plug clip-retaining portion isspaced apart from the mounting flange.
 15. The glow plug of claim 1,wherein the body includes a threaded portion adapted to mount to a modelengine.
 16. The glow plug of claim 1, wherein the indentation is aknurl.
 17. The glow plug of claim 1, wherein the body includes an outerdiameter of about 0.33 inch (0.84 cm) to 0.35 inch (0.89 cm).
 18. Theglow plug of claim 1, wherein the indentation defines a slot diameter ofthe body of about 0.295 inch (0.75 cm) to 0.325 inch (0.83 cm).
 19. Aglow plug for use in a model engine and for connecting to a glow plugclip, the glow plug comprising a conductor, and a body coupled to theconductor, the body including an outer surface and glow plugclip-retaining portion extending circumferentially about the outersurface.
 20. The glow plug of claim 19, wherein the indentation is asemicircular shaped groove in the body.
 21. The glow plug of claim 19,wherein the indentation is a plurality of grooves in the body.
 22. Theglow plug of claim 19, wherein the body includes an outer surface facingaway from the longitudinal axis, a top end, a bottom end, and a firstslot wall, the first slot wall includes spaced-apart first and secondends, the first slot wall extends along an angle so that the second endof the first slot wall is positioned to lie between the first end of thefirst slot wall and the longitudinal axis, and the first slot walldefines the indentation.
 23. The glow plug of claim 22, wherein the bodyfurther includes a second slot wall that includes spaced-apart first andsecond ends, the second slot wall extends along an angle so that thesecond end of the second slot wall is positioned to lie between thefirst end of the first slot wall and the longitudinal axis, and thefirst and second slot walls define the indentation.
 24. The glow plug ofclaim 23, wherein the second ends of the first and second slot wallsconverge at a center of the indentation.
 25. The glow plug of claim 22,wherein the body further includes a retaining lip positioned to liebetween the top end of the body and the first end of the first slotwall.
 26. The glow plug of claim 22, wherein the body further includes aglow plug clip-engaging surface having spaced-apart first and secondends, the second end of the glow plug clip-engaging surface ispositioned to lie between the longitudinal axis and the first end of theglow plug clip-engaging surface.
 27. The glow plug of claim 26, whereinthe second end of the glow plug clip-engaging surface is contiguous withthe top end of the body.
 28. The glow plug of claim 26, wherein the bodyfurther includes a retaining lip positioned to lie between the first endof the first slot wall and the first end of the glow plug clip-engagingsurface.
 29. The glow plug of claim 19, wherein the indentation thatdefines the glow plug clip-retaining portion is spaced apart from theinner pole.
 30. The glow plug of claim 19, wherein the body includes amounting flange adapted to mount to a model engine and the indentationthat defines the glow plug clip-retaining portion is spaced apart fromthe mounting flange.
 31. The glow plug of claim 19, wherein the bodyincludes a threaded portion adapted to mount to a model engine.
 32. Theglow plug of claim 19, wherein the indentation is a knurl.
 33. The glowplug of claim 19, wherein the body includes an outer diameter of about0.33 inch (0.84 cm) to 0.35 inch (0.89 cm).
 34. The glow plug of claim19, wherein the indentation defines a slot diameter of the body of about0.295 inch (0.75 cm) to 0.325 inch (0.83 cm).
 35. A glow plug for use ina model engine and for connecting to a glow plug clip, the glow plugcomprising a coil having spaced apart first and second ends, a firstconductor coupled to the first end of the coil, and a second conductorcoupled to the second end of the coil, the second conductor including abody and a glow plug clip-retaining portion, and the glow plugclip-retaining portion being defined by an indentation in the body. 36.The glow plug of claim 35, wherein the indentation is a semi-circularshaped groove in the body.
 37. The glow plug of claim 35, wherein theindentation is a plurality of grooves in the body.
 38. The glow plug ofclaim 37, wherein the plurality of grooves extend circumferentiallyaround the body.
 39. The glow plug of claim 35, wherein the bodyincludes an outer surface facing away from the longitudinal axis, a topend, a bottom end, and a first slot wall, the first slot wall includesspaced-apart first and second ends, the first slot wall extends along anangle so that the second end of the first slot wall is positioned to liebetween the first end of the first slot wall and the longitudinal axis,and the first slot wall defines the indentation.
 40. The glow plug ofclaim 39, wherein the body further includes a second slot wall thatincludes spaced-apart first and second ends, the second slot wallextends along an angle so that the second end of the second slot wall ispositioned to lie between the first end of the first slot wall and thelongitudinal axis, and the first and second slot walls define theindentation.
 41. The glow plug of claim 40, wherein the second ends ofthe first and second slot walls converge at a center of the indentation.42. The glow plug of claim 39, wherein the body further includes aretaining lip positioned to lie between the top end of the body and thefirst end of the first slot wall.
 43. The glow plug of claim 39, whereinthe body further includes a glow plug clip-engaging surface havingspaced-apart first and second ends, the second end of the glow plugclip-engaging surface is positioned to lie between the longitudinal axisand the first end of the glow plug clip-engaging surface.
 44. The glowplug of claim 43, wherein the second end of the glow plug clip-engagingsurface is contiguous with the top end of the body.
 45. The glow plug ofclaim 43, wherein the body further includes a retaining lip positionedto lie between the first end of the first slot wall and the first end ofthe glow plug clip-engaging surface.
 46. The glow plug of claim 35,wherein the indentation extends circumferentially about the body. 47.The glow plug of claim 35, wherein the indentation that defines the glowplug clip-retaining portion is spaced apart from the inner pole.
 48. Theglow plug of claim 35, wherein the body includes a mounting flangeadapted to mount to a model engine and the indentation that defines theglow plug clip-retaining portion is spaced apart from the mountingflange.
 49. The glow plug of claim 35, wherein the body includes athreaded portion adapted to mount to a model engine.
 50. The glow plugof claim 35, wherein the indentation is a knurl.
 51. The glow plug ofclaim 35, wherein the body includes an outer diameter of about 0.33 inch(0.84 cm) to 0.35 inch (0.89 cm).
 52. The glow plug of claim 35, whereinthe indentation defines a slot diameter of the body of about 0.295 inch(0.75 cm) to 0.325 inch (0.83 cm).
 53. A glow plug for use in a modelengine and for connecting to a glow plug clip, the glow plug comprisinga coil having spaced apart first and second ends, a first conductorcoupled to the first end of the coil, and a second conductor coupled tothe second end of the coil, the second conductor including a body and aglow plug clip-retaining portion that extends circumferentially aboutthe body.
 54. The glow plug of claim 53, wherein the indentation is asemi-circular shaped groove in the body.
 55. The glow plug of claim 53,wherein the indentation is a plurality of grooves in the body.
 56. Theglow plug of claim 53, wherein the body includes an outer surface facingaway from the longitudinal axis, a top end, a bottom end, and a firstslot wall, the first slot wall includes spaced-apart first and secondends, the first slot wall extends along an angle so that the second endof the first slot wall is positioned to lie between the first end of thefirst slot wall and the longitudinal axis, and the first slot walldefines the indentation.
 57. The glow plug of claim 56, wherein the bodyfurther includes a second slot wall that includes spaced-apart first andsecond ends, the second slot wall extends along an angle so that thesecond end of the second slot wall is positioned to lie between thefirst end of the first slot wall and the longitudinal axis, and thefirst and second slot walls define the indentation.
 58. The glow plug ofclaim 57, wherein the second ends of the first and second slot wallsconverge at a center of the indentation.
 59. The glow plug of claim 56,wherein the body further includes a retaining lip positioned to liebetween the top end of the body and the first end of the first slotwall.
 60. The glow plug of claim 56, wherein the body further includes aglow plug clip-engaging surface having spaced-apart first and secondends, the second end of the glow plug clip-engaging surface ispositioned to lie between the longitudinal axis and the first end of theglow plug clip-engaging surface.
 61. The glow plug of claim 60, whereinthe second end of the glow plug clip-engaging surface is contiguous withthe top end of the body.
 62. The glow plug of claim 60, wherein the bodyfurther includes a retaining lip positioned to lie between the first endof the first slot wall and the first end of the glow plug clip-engagingsurface.
 63. The glow plug of claim 53, wherein the indentation thatdefines the glow plug clip-retaining portion is spaced apart from theinner pole.
 64. The glow plug of claim 53, wherein the body includes amounting flange adapted to mount to a model engine and the indentationthat defines the glow plug clip-retaining portion is spaced apart fromthe mounting flange.
 65. The glow plug of claim 53, wherein the bodyincludes a threaded portion adapted to mount to a model engine.
 66. Theglow plug of claim 53, wherein the indentation is a knurl.
 67. The glowplug of claim 53, wherein the body includes an outer diameter of about0.33 inch (0.84 cm) to 0.35 inch (0.89 cm).
 68. The glow plug of claim53, wherein the indentation defines a slot diameter of the body of about0.295 inch (0.75 cm) to 0.325 inch (0.83 cm).